No specific info about version 4.0. Please visit the main page of ThumbsPlus on Software Informer.
Have used this program for years alongside Picasa and GIMP with no problems at all.
I see ThumbsPlus and Picasa as complementary. Picasa has some indexing tricks e.g. face matching, that ThumbsPlus does not but overall can't come near ThumbsPlus.
It's a very good, stable piece of software.
Been using this prog since it was first released and have always found it perfect for my requirements.
ThumbsPlus equals perfect pictures.